Pulmonary fibrosis is a detrimental component of many disorders. The long standing focus of my laboratory has been the examination of adenosine signaling in pulmonary fibrosis with the goal of promoting novel therapies for diseases exhibiting uncontrollable fibrosis. In previous cycles of this grant we have shown that adenosine levels are elevated in interstitial lung diseases where fibrosis is prominent and define adenosine as a pro-fibrotic signal through engagement of the A2B adenosine receptor (A2BR). Furthermore, we found that A2BR signaling promotes the production of interleukin-6 (IL-6) in alveolar macrophages of mice with progressive pulmonary fibrosis, and in M2 macrophages isolated from IPF patients. We have new evidence that blockade of IL-6 signaling in mouse models of adenosine-dependent pulmonary fibrosis leads to diminished fibrosis. Furthermore, examination of STAT-3 activation identified alveolar epithelial cells (AECs) as potential IL-6 targets in these models. Additional preliminary data demonstrate increased levels of the soluble IL-6Ra (sIL-6Ra) in lavage fluid of mice and humans with pulmonary fibrosis suggesting that IL-6 trans signaling may contribute to fibrotic properties. These findings led to the hypothesis that A2BR-dependent production of IL-6 from macrophages contributes to pulmonary fibrosis by inducing epithelial mesenchymal transition in AECs in an IL-6 trans signaling and STAT-3-dependent manner. Three Aims are designed to test this hypothesis: Aim 1. Examine A2BR-dependent IL-6 production as a mechanism for promoting pulmonary fibrosis; Aim 2. Examine mechanisms by which IL-6 influences pulmonary fibrosis; and Aim 3. Examine A2BR-mediated production of IL-6, shedding of IL-6R and STAT-3 activation in IPF patients. These studies will lead to novel and important pre-clinical data to support a role for A2BR antagonism and IL-6 neutralization as therapeutics for pulmonary fibrosis.